Method of stabilizing chlorinated aliphatic hydrocarbons



Patented July 4, 1933 j UNITED STATES PATENT-. oFFis LEROY O. STEWART AND LEE DE FREE, OF MIDLAND, MICHIGAN, ASSIGNORS'TO' TEE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN METHOD OF STABITIIZING CHLORINATED ALIPEATIG HYDBOGARBONS No Drawing.

The invention relates to methods of inhibiting the decomposition of chlorinated al1- phatic hydrocarbons and to the improved product thereby obtained.

. The marked tendency. of chlorinated aliphatic hydrocarbons, e. g. carbon tetrachlo ride, tetrachloroethylene, propylene chloride, etc. toward decomposition during storage and/or distillation, particularly in the presenceof moisture, is well known. In general this tendency toward decomposition is more chlorinated hydrocarbons corrosive 'proppronounced when such hydrocarbons are in contact with copper, as during distillation in dry cleaning solvent recovery, etc. Furthermore, in connection with the distillation of the aforementioned chlorinated hydrocarbons in copper recovery stills, it has been shown that by inter-action between the decomposition products of the hydrocarbons and the metal of the still,'co pper salts are formed which markedly accelerate the decompositlon of the hydrocarbon. Thus the rate at which the solvent breaks down increases progressively when in contact with copper. Such decomposition quite generally imparts to the erties which render them objectionable for many purposes.

To overcome this difficulty it has been pro' posed to add to the chlorinated hydrocarbons certain materials which are capable of 1nh1b1ting the tendency thereof toward-decomposr tion. For example, chlorinated allphatic hydrocarbons having incorporated therewith compounds such as benzaldehyde, cyclohexane, various dyes, petroleum oil fractions,

toluene, etc: have been proposed as compost tions of matter wherein the tendency o f chlorinated hydrocarbon toward decomposltlon 1 s suppressed. However, the use as decom cs1- tion inhibitors of-compounds such as the oregoing has been disadvantageous, prlncipally because of the relatively large proportion of the inhibitor that must be included with the chlorinated hydrocarbon to render it efliectlve. Other disadvantages, suchas coloration of the mixture of inhibitor and hydrocarbon, as I in the case of dyes; separation of the inhibitor and hydrocarbon during distillation, as in the case of benzaldehyde, etc.; have attached to 1932. Serial No. 618,693.

the use of the type of inhibitors, hereinbefore recited.

We have now found that chlorinated aliphatic hydrocarbons can be rendered stable I during storage and distillation, particularly several approved combinations of ingredients embodylng our invention, such disclosed [means constituting, however, but several of various forms in which the principle of the invention may be used.

The proportions of the mercaptan, which we have found suflicient in admixture with chlorinated aliphatic hydrocarbons to suppress decomposition, is exceedingly small, e. g. between about 0.001 and 0.1 per cent by volume. The selection of the mercaptan in any particular instance will be determined somewhat by the boiling point of the hydro--' carbon, since it is'desirable that the boiling point of the mercaptan and that of the hydrocarbon'be reasonably close together in order that the mercaptan will be retained therein during distillation.

.The following Table I shows the results which have been obtained in practicing our invention, using various mercaptans for inhibiting the decompositions of carbontetrachloride. As a measure of the decomposition occurring in the chlorinated hydrocarbon during contact with copper and iron, we have determined the milligrams of metal corroded away-per square decimeter of area exposed to the action of the hydrocarbon at refluxing temperature'for 46 hours in the presence of water. The tests were conducted by partially immersing a weighed and measured strip of metal in a measured volume of the chlorinated hydrocarbon containing the in,- hibitor in a round-bottomed flask, adding me II Milligrams loss per square decimeter v Hydrocarbon p r No in Mereaphlbltm' tan Carbon tetrachloride 14,800 22" Tetrachloroethylene.- 412 7 orolorm 231 y 70 Trichloroethylenb---- 1 92 25 Propylene chloride 43 l1 as I 507 Carbon tetrachloride 286 Tettachloroethylene-.-

,Car ntetrachlorid 25 50%Trichloroethylene 90% arbon tetrachlorid 23 107 Propylene chloride Mil-Te hl'oroethy lene my 17 10% Propylene-chloride about 40 percent by volume of water to the mixture in the flask, connecting the flask to a refluxing column; and heating the contents of the flask at refluxing temperature. The

amount of inhibitor employed is shown in per cent by volume of the carbon tetrachloride.

.The 'decomposition-inhibiting effect of incorporating approximately 0.005 per cent by volume of n-butyl mer'captan with various chlorinated aliphatic hydrocarbons and mixtures thereof is shown in the following Table II, which also gives as the measure of the decomposition. occurring in the'particular hydrocarbon or mixture the milligrams of copper corroded away per square decimeter of area exposed to the action of the hydrocarbon at refluxing temperature for 46 hours in the presence of water. r

From the foregoing tables it is readily to be seen that the incorporation of a'relatively small amount of La 'mercaptan with chlori-- nated aliphatic hydrocarbons results in a'distinct reduction of the decomposition occurrin in the hydrocarbon when in'c'ontact wit copper or iron even under the extremely severe conditions of continuous refluxing over a 46 hour period of time in the presence 1 of water. Further, we have determined that a similar benefit inures to the aforementioned hydrocarbons from the admixture therewith of-a me'rcaptan when incontact with other metals, e. g. iron,- steel, .tin, .Monel metal,

. composition.

vtween about 0.001 and of a mercaptan.

carbontetrachloride and a such hydrocarbons upon exposure to sunlight is also generally'inhibited in our new be noted is the effect upon Particularly to the decomposltion rate caused by incorporating a mercaptan with carbon tetrachloride, or mixtures thereof with various other chlorinated aliphatic hydrocarbons. The tables show that the addition of only 0.005 per cent of n-butyl mercaptanreduces the amount of corrosion, or, suppresses the decomposition,

substantially inhibited, and such mixtures may safely be stored or shipped in iron or steel containers.

' Among the especially advantageous appli cations which can be made of our improved composition of matter are (1) dry cleaning,

wherein recovery of the solvent composition is accomplishedby distillation; and, vapor phase degreasin of metallic articles.

Other modes of app yifig the principle of our invention maybe employed instead of the one explained, change bemg' made as regards the materials employed, provided the ing're dients stated by any of the following I or the equivalent of such stated ingredients be employed.

We therefore particularly point out and distinctly-claim as our invention claims 1. A- compositionof matter comprising a i chlorinated aliphatic h drocarbon and a relatively small amount 0 a mercaptan.

2. A composition of matter oomprisin a chlorinated aliphatic hydrocarbon and 3. A composition of matter comprising a chlorinated aliphatic hydrocarbon and about 0-0051) cent by volume of n-butyl mer-.v aPtan.

4. A composition of -matter comprising 118mg percent relatively small 0.1 per cent by volume I I 6. A composition-I of matter comprising tetrachloroethylene and a relatively amount ofamercaptan. -7. 'A- composition of matter comprising.

tetrachloroethylene and about 0.005 per cent by volume of n-butyl mercaptan. 8. A composition. of matter comprising trichloroethylene and a relatively. small amount of a mercaptan.

.9. A composition of matter comp triehloroethylene and about 0.005 per cent by J volume-of n-butyl mercaptan.

13. A composition of matter comprisin a chlorinated aliphatic hydrocarbon which as at least two chlorine atoms in the molecule and a relatively small amount of a mercaptan. .14. The method of inhibiting the decomsition of chlorinated aliphatic hydrocarins having, at least two chlorine atoms in the molecule which consists in incorporating therewith a relatively small amount of a mercaptan.

Signed by us this 17th day of June, 1932.

L'EROY C. STEWART. LEE DE FREE. 

